The present invention relates to a technology for conducting a digital copy of image information by means of a digital information compression technology, and more particularly to an apparatus for and a method of controlling image quality reduction of image information for making a copy after image quality of image information is reduced.
In general, there is an MPEG (Moving Picture Image Expert Group) method in a technology for compressing digital information of a moving picture image. When image information to which compression is applied by this MPEG is restored, and a digital copy is made, theoretically it is possible to infinitely and repeatedly make a copy without deteriorating its image quality.
Accordingly, it becomes to be substantially difficult to protect copyrights of all image information that can be an object to be copied.
Therefore, conventionally, a method of electronic transparency and so forth was proposed, in which specific copyright protection information for protecting a copyright was previously generated, and this protection information was stenciled into image information.
According to this method, a function for detecting a data, copy of which is prohibited by the above-described copyright protection information, is provided in a digital copy machine. And, the machine can be constructed so that, when such a data is detected in making a copy, to make a copy is automatically interrupted and a data is deleted if the data is already copied.
Also, an MPEG specification is provided in detail in ISO-13818 and JT-H262. Accordingly, in making a digital copy, a function for processing image information is required, which in principle conforms to these specification provisions.
However, when a digital copy of image information based on the MPEG specification is made by using such a conventional example, it is necessary to previously solve technical tasks as mentioned below.
First, it is necessary that to make a copy under execution is interrupted and a data is deleted if to make a copy of the data is already completed. For that, it becomes to be necessary to control the switching of selection and function of the interruption and deletion, and extremely complicated processing, including an original function of the digital copy, should be executed.
Second, also with regard to a data in a copy prohibition part, if it is not changed within a range that conforms to the MPEG specification, it becomes to be difficult to conduct image processing like a data in other parts. Accordingly, it is impossible to be compatible with reproduction of proper image information by a standard MPEG decoder. Therefore, to solve these technical items as a whole is an important technical task.